Voltage regulated mig welding using a constant current power source

ABSTRACT

A system and method of duplicating CV mode of operation with a CC power includes a wire feeder designed to automatically adjust the speed of which consumable wire is delivered to a weld so as to maintain a target voltage set by a user. The wire feeder is designed to be operational on a CC power source yet automatically adjust the WFS so that a user-selected target voltage is maintained at the weld. A controller within the wire feeder is programmed to read an input from the user to the wire feeder identifying a target voltage and control the speed by which a drive assembly delivers metal filler to the weld based on the target voltage. By automatically adjusting the WFS, the user is not required to manually adjust the WFS to maintain the target voltage at the weld.

BACKGROUND OF INVENTION

The present invention relates generally to welding systems and, moreparticularly, to a wire feeder connected to a constant current (CC)power source and designed to automatically adjust the speed by whichconsumable welding wire is delivered to a weld so as to maintain atarget voltage at the weld.

Wire feeders are typically used to feed metal wire into a weld during awelding process such as Gas Metal Arc Welding (GMAW) and other weldingprocesses. Typical wire feeders have a drive roller assembly for drivingthe metal feed from a feed spindle through a welding gun forintroduction to the weld. Power is supplied to the drive roller assemblyby a welding power supply via a weld cable. The amperage or currentgenerated by the power supply governs the speed in which the metal feedis fed to the weld, or the wire feed speed (WFS). Generally, the higherthe amperage supplied to the wire feeder, the greater the WFS.Conversely, if voltage is used to govern the WFS, the lower the voltage,the higher the WFS. Accordingly, the speed by which the wire feedersupplies the filler metal to the weld is a direct function of the powerdelivered to the wire feeder and therefore, the weld. The thickness ofthe metal being welded determines the power required at the weld andthus the WFS necessary to deliver that power. A thicker metal requireshigher power to effectively weld.

Typically, power sources, which may be designed to supply power to thewire feeder, have been constructed to operate in either a constantcurrent (CC) mode or a constant voltage (CV) mode. For those weldingapplications that require a constant current input to the wire feeder,the wire feeder is connected to a CC power source. Conversely, for thosewelding applications that require a constant voltage at a weld, the wirefeeder is connected to a CV power source. For CC mode of operation, theuser is able to adjust the speed by which metal filler or consumableelectrode is delivered to a weld so as to maintain a desired voltage atthe weld. Conversely, for a CV mode of operation, the user may adjustthe wire feed speed to maintain a target current level at the weld. Wirefeed speed (WFS) and voltage at the weld are inversely related thereforeto increase the arc voltage at the weld, the WFS must be decreased andto lower the voltage at the weld, the WFS must be increased. Incontrast, WFS and current are directly related and, as such, an increasein WFS will cause an increase in current and vice versa.

For most GMAW welding applications, it is necessary that the wire feederbe connected to a CV power source. For example, short circuit transferis a welding application that is characterized by a less than 21 voltarc voltage. With a CV power source, the user is able to set a desiredtarget voltage that may be less than 21 volts and adjust the speed bywhich wire is delivered to the weld to control output current.Accordingly, the user may increase output current by increasing WFSwhile the voltage at the weld is held at the target level by the CVpower source. In contrast, CC power sources are typically not usable forshort circuit transfer applications.

CC power sources are designed to maintain a constant output currentlevel. The user inputs a desired target current level on the powersource and the operational circuitry of the power source operates tomaintain an output current level. The user may then adjust the WFS toregulate a voltage at the weld. To increase the voltage at the weld, theWFS is decreased. To decrease the voltage, the WFS is increased. If theweld is underpowered, the weld will be insufficient to adequately jointhe materials being welded. On the other hand, if the weld isoverpowered, it is possible to “burn through” the materials beingwelded. As such, the user must proactively monitor the weld and adjustthe WFS accordingly.

Typically, however, the wire feeder will control the WFS within alimited range of values. As a result, when the wire feeder is operatingon a CC power source, the user may be unable to get a desired voltagelevel at the weld. For instance, for short circuit transferapplications, an arc voltage of less than 21 volts is generallyrequired. However, achieving an arc voltage of less than 21 volts maynot be possible given the constant current level being maintained by thepower source. That is, at the current level selected by the user,additional power may be needed at the weld to sufficiently fuse thematerials. To increase the power at the weld, the user will decrementthe WFS to increase the arc voltage. Because the wire feeder has alimited range of acceptable WFS values, it may not be possible for theuser to decrement the WFS to a level needed to adequately increase thearc voltage. As a result, the weld is underpowered and the materials maynot be properly fused. Similarly, to prevent “burn through” the user mayseek to increase the WFS to drive the voltage downward to a level thatis not permitted by the wire feeder.

Therefore, to carry out a particular short circuit transfer application,a CV power source may be required which increases equipment costs andaccentuates the under-utilization of the CC power source. Additionally,multiple power sources increases the costs associated with maintenanceas well as storage.

It would therefore be desirable to have a system and method capable ofduplicating CV mode of operation with a CC power source.

BRIEF DESCRIPTION OF INVENTION

The present invention provides a system and method of duplicating CVmode of operation with a CC power source that overcomes theaforementioned drawbacks. The invention includes a wire feeder designedto automatically adjust the speed of which consumable wire is deliveredto a weld so as to maintain a target arc voltage set by a user. The wirefeeder is designed to be operational on a CC power source yet adjust theWFS so that a user-selected target voltage is maintained at the weld. Acontroller within the wire feeder is programmed to read an input fromthe user to a control panel on the wire feeder identifying a targetvoltage and control the speed by which a drive assembly delivers metalfiller to the weld based on the target voltage. The target voltage ispreferably set to a value such that the weld is sufficiently powered toproperly fuse materials at the weld. By automatically adjusting the WFS,the user is not required to manually adjust the WFS to maintain thetarget voltage at the weld.

Therefore, in accordance with one aspect of the present invention, awire feeder for a MIG welding system includes a power input configuredto receive power at a substantially constant current level from a powersource. The wire feeder also includes a drive assembly configured tointroduce a consumable electrode to a weld at a WFS as well as acontroller to set an initial WFS based on a user input. The controlleris also configured to automatically adjust the WFS to reduce adifference between a target arc voltage and an actual arc voltage.

According to another aspect of the present invention, a MIG weldingsystem includes a power source configured to provide a constant currentoutput. The welding system further includes a wire feeder connected toreceive a constant current output and configured to deliver a consumableelectrode to a weld at a WFS and automatically adjust the WFS tomaintain the target voltage at the weld.

In accordance with yet a further aspect of the present invention, acontroller is provided to regulate output of a wire feeder. Thecontroller is programmed to set an initial WFS and a target arc voltagefor a CC welding process. The controller is further programmed tomonitor a voltage level at a weld during the CC welding process andadjust WFS if the voltage level at the weld deviates from the target arcvoltage.

In accordance with another aspect of the present invention, a method ofexecuting a constant current welding process is provided. The methodincludes the steps of receiving voltage feedback of a voltage at a weldand comparing the value of actual voltage at the weld to a targetvoltage. The method further includes a step of adjusting a speed ofwhich consumable welding wire is delivered to the weld to reduce thedifference between actual voltage and the target voltage.

In accordance with yet another aspect of the invention, a controller isconfigured to regulate operating parameters of a wire feeder connectedto a CC power source so as to duplicate a CV welding process on the CCpower source below an arc voltage level of approximately 22 volts.

According to another aspect, the present invention includes a wirefeeder controller configured to receive a user input identifying ascaled representation of a voltage set point and determine a WFS fromthe scaled representation of the voltage set point.

Various other features, objects and advantages of the present inventionwill be made apparent from the following detailed description and thedrawings.

BRIEF DESCRIPTION OF DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a perspective view of a welding system.

FIG. 2 is a sectional view of the wire feeder taken along lines 2-2 ofFIG. 1.

FIG. 3 is a front elevational view of a control panel of the wire feederillustrated in FIG. 1.

FIG. 4 is a flow chart setting forth the steps of a control algorithmcarried out by a controller in the wire feeder for maintaining a targetarc voltage based on a user input to the control panel illustrated inFIG. 2.

DETAILED DESCRIPTION

Referring to FIG. 1, a welding-type system 10 is shown incorporating thepresent invention. System 10 includes a power source 12, which can be anAC or a DC welding power supply operable in a constant current (CC)mode. The power source 12 has a work cable 14 and clamp 16 designed tohold a workpiece 18 for welding. Power source 12 is connected to a wirefeeder 20 via cable 22. Connected between the power source 12 and thewire feeder 20 is a weld cable 22. The wire feeder 20, which in oneembodiment is portable, also includes a welding torch or gun 24 and avoltage sensing lead with clip 26 configured to provide voltage at theweld feedback to the wire feeder. A shielding gas cylinder 28 is alsoconnected to the wire feeder 20 to provide shielding gas for the weldingprocess.

When the welding torch 24 is positioned proximate to workpiece 18,welding wire is fed into contact with the workpiece 18. Once triggered,an electrical current and voltage are generated to cause the weldingwire to be heated and melt. As a result, an electrical arc isestablished which causes the welding wire to continue to melt as well astransfer the melted welding wire to the workpiece 18 where the weldingwire fuses and cools with the workpiece 18. Because the electricalenergy supplied to the welding system is typically greater than thatrequired to melt the welding wire, most of the remaining energy is inthe form of heat which is transferred to the surface of the workpiece 18resulting in the workpiece 18 also melting and improving bonding betweenthe melted welding wire and the workpiece 18. As the welding torch 24 istranslated across the workpiece 18, melted welding wire is continuouslytransferred to the workpiece 18. The wire feeder is designed tointroduce flux cored, solid steel, or stainless steel welding wire to aweld. One skilled in the art would appreciate that these value areillustrative of only one particular welding assembly and that thepresent invention is equivalently applicable with other welding systemshaving different operating specifications.

Referring now to FIG. 2, the wire feeder 20 includes a wire driveassembly 30 to drive wire from a spool 32 designed to support weldingwire (not shown) that is supplied to the weld under control of acontroller 34 embodied in operational circuitry secured to a circuitboard 34 that is connected to the power source 12 through cord 22,FIG. 1. The controller is governed by a microprocessor capable of beingprogrammed to operate according to certain algorithms and/or programs.User selections or inputs received by the controller from a display andcontrol panel, FIG. 3, and an internally programmed algorithm causewelding system 10 to operate according to the user selections.

Referring now to FIG. 3, a front elevational view of a control panel ofa wire feeder is illustrated. Control panel 36 is designed to allow theuser to input various welding parameters so as to define the weldingprocess to be carried out. Specifically, the control panel includes aON/OFF switch 38 that allows the user to switch the wire feeder on oroff. Control panel 36 also includes a JOG/PURGE button or switch 40 thatallows the user to purge or remove existing gas from the wire feeder.That is, the wire feeder includes a controller that detects activationof purge button 40 and in response thereto transmits a control signal tothe gas valve assembly of the wire feeder to cause the drive assembly topurge any residual gas from the wire feeder. Control panel 36 alsoincludes a JOG button that when selected causes the controller withinthe wire feeder to transmit a jog command to the drive assembly.

Control panel 36 also provides a user interface on the wire feeder thatallows the user to set a target voltage via knob 42 as well as aninitial wire feed speed via knob 44. One skilled in the art willappreciate that the functionality achieved with dual knobs 42 and 44 mayalso be achieved with a single telescoping knob. As will be described ingreater detail below, the wire feed controller will regulate the driveassembly such that the target voltage selected via the user by adjustingknob 42 is substantially maintained at the weld. Additionally, thecontroller, based on user adjustment of wire feed speed knob 44, willset an initial speed by which welding wire is to be delivered to theweld. However, as will be described in greater detail below, thecontroller, based on feedback received from the weld, will automaticallyadjust the wire feed speed so that the target voltage selected by theuser is maintained. It should be noted, in one embodiment, that a legend46 associated with voltage adjustment knob 42 represents a scaledvoltage level of the desired target voltage. That is, user adjustment ofknob 42 to reference numeral 2 of legend 46 represents that the userdesires the target voltage to be 20V.

Control panel 36 illustrated in FIG. 3 represents an example of acontrol panel which may be incorporated in the wire feeder. One skilledin the art will readily appreciate that the appearance and/ororientation of the selector switches, knobs, buttons, and the like maydiffer from that specifically illustrated. Additionally, LCDs and LEDs(not specifically shown) may also be utilized and are considered withinthe scope of the present invention. For example, control panel 36 may beconstructed such that an LCD displays one or more menus that allow theuser to interactively set the target arc voltage as well as the initialwire feed speed. In this regard, the user may navigate through a seriesof menus or windows that are displayed on the LCD in defining theoperational parameters of the welding process to be carried out.

As noted above, the present invention provides a controller that isconfigured to automatically adjust the speed by which a consumableelectrode is delivered to a weld so that a user selected target voltageis maintained. As such, a relatively constant arc voltage is achieved inaddition to the constant current input provided to the wire feeder fromthe CC power source. Referring now to FIG. 4, a control technique oralgorithm 50 for automatically maintaining a relatively constant voltageat a weld achieved by a controller within a wire feeder connected to aCC power source is illustrated. The technique or process 50 begins atstep 52 with a user setting a constant current level on a CC powersource as well as setting an initial wire feed speed and target voltageon a control menu on the wire feeder such as that illustrated in FIG. 3.The controller within the wire feeder executing process 50 then sets theinitial WFS and target voltage based on the user selected inputs. Thecontroller will then transmit a control signal to the drive assembly ofthe wire feeder such that wire is fed to the weld at a speed equal tothat identified by the user input. Once the welding process commences,the controller will monitor voltage at the weld at step 56 based onvoltage feedback. From the feedback, the controller will compare theactual arc voltage or voltage at the weld to the target voltage input bythe user to the control menu. If the actual voltage at the weld exceedsthe target voltage 58, 60, the controller will send a control signal tothe drive assembly of the wire feeder causing an increase in WFS 62.Because voltage and WFS have an inverse relationship, an increase in theWFS will cause a decrease in the actual voltage. As such, the controlsignal transmitted to the drive assembly by the controller is designedto cause the drive assembly to increase the WFS to a level sufficient todrive the actual voltage to the target voltage level. As such, thedifference between the actual voltage and the desired target voltage isreduced and, preferably, brought to zero.

If the actual arc voltage does not exceed the target voltage desired bythe user 58, 64, the controller then determines if the actual voltage isless than the target voltage 66. If so 66, 68, the controller transmitsa control signal to the wire drive assembly causing the drive assemblyto decrease the speed by which the consumable electrode or welding wireis delivered to the weld 70. As noted above, voltage and WFS areinversely related; therefore, a decrease in WFS causes an increase involtage. As such, the controller instructs the drive assembly todecrement the WFS to a level that will cause an increase in arc voltageto a level that reduces the difference between the target voltage andthe actual arc voltage. Whether there is an increase in WFS, a decreasein WFS, or no change in the WFS, process 50 returns to step 56 withcontinued monitoring of the arc voltage. The monitoring andincrement/decrement loop will be repeated throughout the welding processuntil the welding process ends at 74.

In an alternate embodiment, the controller may execute process 50 suchthat a comparison to a threshold value is carried out before anadjustment in WFS occurs. That is, the controller may compare thedifference between actual arc voltage and the target arc voltage with anerror threshold to first determine whether the difference between theactual and target voltages is at a level sufficient to cause a change inWFS. For instance, the controller and the wire feeder may be programmedsuch that a change in WFS command is not transmitted to the driveassembly until the absolute value of the difference between an actualarc voltage and target arc voltage exceeds one-half volt. In thisregard, a minor below threshold deviation from the target voltage as aresult of a transient condition will not cause a change in the WFS.

In yet another embodiment, the controller in executing process 50 may beprogrammed to execute a timing loop that determines if the differencebetween actual voltage and target voltage while not sufficient towarrant a change in WFS initially may be maintained over a significanttime interval thereby indicating that the minor difference in actualvoltage compared to target voltage has not been caused by a transientcondition and is therefore indicative of a more permanent systemcondition. In this regard, the controller may then instruct the driveassembly to increment/decrement the wire feed speed despite thedifference between actual voltage and target voltage being less than theset threshold.

Therefore, in accordance with one embodiment of the present invention, awire feeder for a MIG welding system includes a power input configuredto receive power at a substantially constant current level from a powersource. The wire feeder also includes a drive assembly configured tointroduce a consumable electrode to a weld at a WFS as well as acontroller to set an initial WFS based on a user input. The controlleris also configured to automatically adjust the WFS to reduce adifference between a target arc voltage and an actual arc voltage.

According to another embodiment of the present invention, a MIG weldingsystem includes a power source configured to provide a constant currentoutput. The welding system further includes a wire feeder connected toreceive a constant current output and configured to deliver a consumableelectrode to a weld at a WFS and automatically adjust the WFS tomaintain the target voltage at the weld.

In accordance with yet a further embodiment of the present invention, acontroller is provided to regulate output of a wire feeder. Thecontroller is programmed to set an initial WFS and a target arc voltagefor a CC welding process. The controller is further programmed tomonitor a voltage level at a weld during the CC welding process andadjust WFS if the voltage level at the weld deviates from the target arcvoltage.

In accordance with another embodiment of the present invention, a methodof executing a constant current welding process is provided. The methodincludes the steps of receiving voltage feedback of a voltage at a weldand comparing the value of actual voltage at the weld to a targetvoltage. The method further includes a step of adjusting a speed ofwhich consumable welding wire is delivered to the weld to reduce thedifference between actual voltage and the target voltage.

In accordance with yet another embodiment of the invention, a controlleris configured to regulate operating parameters of a wire feederconnected to a CC power source so as to duplicate a CV welding processon the CC power source below an arc voltage level of approximately 22volts.

According to another embodiment, the present invention includes a wirefeeder controller configured to receive a user input identifying ascaled representation of a voltage set point and determine a WFS fromthe scaled representation of the voltage set point.

As one skilled in the art will fully appreciate, the heretoforedescription of welding devices not only includes welders, but alsoincludes any system that requires high power outputs, such as heatingand cutting systems. Therefore, the present invention is equivalentlyapplicable with any device requiring high power output, includingwelders, plasma cutters, induction heaters, and the like. Reference towelding power, welding-type power, or welders generally, includeswelding, cutting, or heating power. Description of a welding apparatusillustrates just one embodiment in which the present invention may beimplemented. The present invention is equivalently applicable with manyhigh power systems, such as cutting and induction heating systems, orany similar systems.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A wire feeder for an MIG welding system, the wire feeder comprising:a power input configured to receive power at a substantially constantcurrent level from a power source; a drive assembly configured tointroduce a consumable electrode to a weld at a wire feed speed; and acontroller to set an initial wire feed speed based on a user input andautomatically adjust the wire feed speed to reduce a difference betweena target arc voltage and an actual arc voltage.
 2. The wire feeder ofclaim 1 wherein the controller is further configured to compare theactual arc voltage to the target arc voltage, set by a user, and, fromthe comparison, incrementally adjust the wire feed speed.
 3. The wirefeeder of claim 2 wherein the controller is further configured todecrease the wire feed speed if the actual arc voltage is less than thetarget arc voltage.
 4. The wire feeder of claim 2 wherein the controlleris further configured to increase the wire feed speed if the target arcvoltage is less than the actual arc voltage.
 5. The wire feeder of claim1 wherein the controller is further configured to continuously monitorarc voltage during an MIG welding process.
 6. The wire feeder of claim 1further comprising a control panel configured to allow a user to selectthe initial wire feed speed and a scaled target arc voltage.
 7. An MIGwelding system comprising: a power source configured to provide aconstant current output; and a wire feeder connected to receive theconstant current output and configured to deliver a consumable electrodeto a weld at a wire feed speed and automatically adjust the wire feedspeed to maintain a target voltage at the weld.
 8. The MIG weldingsystem of claim 7 wherein the wire feeder includes a menu designed toenable a user to input a desired target voltage and further includes acontroller designed to read the input.
 9. The MIG welding system ofclaim 7 wherein the wire feeder includes a controller configured tocompare an actual voltage at the weld to the target voltage and adjustthe wire feed speed to minimize a difference between the actual voltageand the target voltage.
 10. The MIG welding system of claim 9 whereinthe controller of the wire feeder is further configured to increase thewire feed speed if the actual voltage exceeds the target voltage. 11.The MIG welding system of claim 10 wherein the controller of the wirefeeder is further configured to decrease the wire feed speed if thetarget voltage exceeds the actual voltage.
 12. The MIG welding system ofclaim 7 wherein the wire feeder includes a voltage sensed wire feederdesigned to at least operate based on voltage feedback from the weld.13. A controller to regulate output of a wire feeder, the controllerprogrammed to: set an initial wire feed speed and a target arc voltagefor a constant current (CC) welding process; monitor a voltage level ata weld during the CC welding process; and adjust wire feed speed if thevoltage level at the weld deviates from the target arc voltage.
 14. Thecontroller of claim 13 further programmed to increase the wire feedspeed if the voltage level at the weld is greater than the target arcvoltage and decrease the wire feed speed if the voltage level at theweld is less than the target arc voltage.
 15. The controller of claim 13further programmed to receive a number of inputs from a user, and setthe initial wire feed speed and the target arc voltage from the numberof inputs.
 16. The controller of claim 13 incorporated into a portablewire feeder configured to introduce consumable welding wire to the weld.17. The controller of claim 16 wherein the wire feeder includes a driveassembly configured to introduce the consumable wire to the weld at avariable wire feed speed.
 18. The controller of claim 16 wherein theportable wire feeder is further configured to receive a CC power inputfrom a power source.
 19. A method of executing a constant currentwelding process, the method comprising the steps of: receiving voltagefeedback of voltage at a weld; comparing a value of actual voltage atthe weld to a target voltage; and adjusting a speed of which consumablewelding wire is delivered to the weld to reduce a difference between theactual voltage and the target voltage.
 20. The method of claim 19wherein the step of adjusting includes the steps of: increasing thespeed if the actual voltage exceeds the target voltage; or decreasingthe speed if the target voltage exceeds the actual voltage.
 21. Acontroller configured to regulate operating parameters of a wire feederconnected to a CC power source so as to duplicate a CV welding processon the CC power source below an arc voltage level of approximately 22volts.
 22. A wire feeder controller configured to: receive a user inputidentifying a scaled representation of a voltage set point; anddetermine a WFS from the scaled representation of the voltage set point.